Radio frequency identification (RFID) tags and radio frequency identification tag systems are known, and find numerous uses. For example, radio frequency identification tags are frequently used for personal identification in automated gate sentry applications protecting secured buildings or areas. Information stored on the radio frequency identification tag identifies the person seeking access to the secured building. A radio frequency identification tag system conveniently provides for reading the information from the radio frequency identification tag at a small distance using radio frequency (RF) data transmission technology. Most typically, the user simply holds or places the radio frequency identification tag near a base station that transmits an excitation signal to the radio frequency identification tag powering circuitry contained on the radio frequency identification tag. The circuitry, responsive to the excitation signal, communicates the stored information from the radio frequency identification tag to the base station, which receives and decodes the information. In general, radio frequency identification tags are capable of retaining and, in operation, transmitting a substantial amount of information--sufficient information to uniquely identify individuals, packages, inventory and the like.
A typical technology for powering and reading a radio frequency identification tag is inductive coupling or a combination of inductive power coupling and capacitive data coupling. Inductive coupling utilizes a coil element in the radio frequency identification tag. The coil element is excited (or "energized") by an excitation signal from the base station to provide power to the radio frequency identification tag circuitry. The radio frequency identification tag coil, or a second tag coil, may be used to transmit and receive the stored information between the radio frequency identification tag and the base station. Radio frequency identification tags relying on inductive coupling are sensitive to orientation of the radio frequency identification tag with respect to the base station since the field created by the excitation signal must intersect the coil element at substantially a right angle for effective coupling. Read ranges for inductively coupled devices are generally on the order of several centimeters. Longer read distances are desirable, and for certain applications, such as electronic animal identification, baggage tracking, parcel tracking and inventory management applications, are necessary.
Another technology for powering and reading radio frequency identification tags is electrostatic coupling such as employed in the radio frequency identification tag systems and radio frequency identification tags disclosed in the above referenced applications. These systems advantageously provide for substantially increased read/write distances over those available in the prior art. Another advantage derived from the use of the systems and tags therein disclosed is that the user need not bring the radio frequency identification tag in close proximity to a base station or to substantially orient the tag with respect to the base station. It is therefore possible to incorporate the antenna elements of the base station into, for example, a doorway or a vestibule, a package conveyer or an article sorting system, and to energize the tag and read the tag information at a greater distance.
To couple either the inductive or electrostatic signals between the base station and the radio frequency identification tag, the tag necessarily includes an antenna having at least one and frequently two antenna elements. Typically, a tag circuit chip and the antenna are electrically coupled and bonded to a tag substrate. The tag dimensions, governed by the tag substrate dimensions, are typically maintained fairly small. Therefore, the antenna is generally size limited. A smaller antenna, however, adversely affects read ranges. Also, the antenna is necessarily formed co-planar with the tag substrate potentially making the tag orientation sensitive. Because it is undesirable and generally impractical to make the radio frequency identification tag larger, effective antenna size remains limited. And, the typical flat tag design also limits the antenna to a flat, orientation sensitive configuration.
To date radio frequency identification tags have been manufactured as self-contained units, i.e., tag circuit chip, antenna and substrate as a singular package. Therefore, not only has the size and configuration of the antenna posed problems with performance of the radio frequency identification tag, the antenna contributes significantly to the cost of a completed tag.
Applications for radio frequency identification tags include personal identification badges, article and/or package identification tags, and electronic article surveillance tags. In many of these applications, the identification badge, the article and/or package is substantially larger than the radio frequency identification tag used to provide the identifying information. However, the size of the identification badge, article or package has not offered an opportunity for increasing the size or reducing the orientation sensitivity of the antenna of a self-contained radio frequency identification tag.
Thus, there is a need for an improved radio frequency identification tag.